\begin{tikzpicture}[>=Stealth]
    \draw [->] (-3.5,0) -- (3.5,0) node[anchor=north] {$x$};
    \draw [->] (0,-2) -- (0,2) node[anchor=east] {$y$};
    \node at (0.3,-0.3) {$O$};
    \draw [name path=a1] (0,0) .. controls(1,1.5) and (2,1) .. (2,0.8);
    \path [name path=a2] (1,0) -- (1,2);
    \draw [name intersections={of=a1 and a2, by=A}]
        let \p1 = (A)
        in (\x1,\y1) -- (\x1,0) node[anchor=north] {a}
           (-\x1,-\y1) -- (-\x1,0) node[anchor=south] {-a};
    \draw [rotate=180](0,0) .. controls(1,1.5) and (2,1) .. (2,0.8);
    \node at (1.5,1.3) {$P = (a, f(a))$};
    \node at (-1.5,-1.3) {$P = (-a, f(-a))$};
\end{tikzpicture}